The present invention relates to a retrieval apparatus for retrieving information in a data storage medium especially for retrieving information in a data storage medium such as an optical disc.
As one of known retrieval systems using an optical disc, there is known a so-called electronic book wherein information is retrieved in accordance with predetermined retrieval systems. In one optical disc used with such a system there are recorded a plurality of documents such as an English-English dictionary and a biographical dictionary each of which is selected and retrieved in accordance with one or plural retrieval systems such as a forward coincidence system and a condition retrieval system. According to a conventional retrieval apparatus, after selection of one retrieval system, a retrieval character train (word) is inputted, for example, inputted in accordance with a forward coincidence retrieval system as shown in FIG. 10 where the current inputted character train is displayed on a screen. In addition, on the; screen there are displayed a deletion function for erasing the inputted character train, a return function for interrupting the input of the retrieval character train and a retrieval function for retrieving the inputted character train. These three functions can be effected by operating function keys on a keyboard, not shown. When the operator indicates the retrieval function, the retrieval apparatus retrieves index information on the optical disc to check whether items corresponding to the inputted character train exist in the index information on the optical disc. If the items exist, the retrieval apparatus displays all the items on the screen and, if the items do not exist in the index information, the apparatus displays that the corresponding item does not exist.
There is a problem which arises with such a conventional retrieval apparatus, however, in that, if a character train "chrsamthenum" is inputted by mistake in the case that a character train "chrsamthemum" should be inputted as a retrieval character train, difficulty is encountered to check the meaning or content of the retrieval character train. That is, according to the conventional retrieval apparatus, only after retrieval and display of the corresponding item, it can be checked whether the inputted character train is effective or appropriate as a retrieval character train. In other words, if the item corresponding to the inputted character train does not exist, it is impossible to obtain the information indicative of the effective retrieval character train. This causes inconvenience for the user or operator.